It is proposed to study the role of aromatic nitro compounds as potential carcinogens. The aromatic nitro compounds are metabolised to N-oxides, N-hydroxy compounds and amines, supposedly by sequential reduction mechanisms. N-hydroxy derivatives of aromatic amines have been suggested as proximate carcinogens. The metabolism of five or six monocyclic and polycyclic aromatic nitro compounds will be studied. The metabolites will be isolated and characterized by conventional and modern analytical techniques. Studies will also include the characterization of the enzyme system or systems (nitro-reductases) responsible for the metabolism of aromatic nitro groups. In addition, the urinary and plasma levels of the metabolites will be correlated with methemoglobinaemia and incidence of bladder tumors in experimental animals.